The present invention relates generally to video tape recording systems, and, more particularly, to such systems in which multiple segments of video information are to be recorded on a tape sequentially, but at time-spaced intervals.
When a video tape recorder is employed to record television programs, it is typically run in a recording mode for relatively long, uninterrupted periods of time. Moreover, a recorder used to record television programs will only rarely be operated in playback mode in such a manner that two or more recorded program segments are played back without stopping the tape. However, when a recorder is utilized in conjunction with a video camera, in what might be referred to as a "home movie" mode of operation, the recorder will be started and stopped very frequently, and the recorded scene length will typically be only several seconds long.
Tape transport apparatus used in video recording systems require a significant time interval to accelerate the tape to recording speed, and to decelerate the tape when recording is to be stopped. If the tape is merely decelerated at the end of the recording of one scene, and accelerated again at the beginning of the recording of the next scene, line and field synchronizing signals recorded on the tape with the video information would be unevenly spaced along the tape. Even if recording was suppressed during the tape acceleration and deceleration times, there would be a significant discontinuity in the sequence of synchronization signals. Consequently, if the tape was to be played back at full speed, there would be a temporary loss of synchronization in the reproduced video image, and an accompanying roll of the picture image at each scene change. Since the scenes may be only several seconds long, these frequent losses of synchronization would be a continual source of inconvenience and annoyance to viewers of the system.
In recorders of the helical scan type, the aforedescribed problem has been solved by back-spacing the recorder on completion of one scene; then, on starting recording of the next scene, synchronizing the camera with the video material recorded at the end of the previous scene before switching to the recording mode. However, in helical scan recorders, it may take as long as five or six seconds to bring the tape transport apparatus up to recording speed and to lock onto the synchronization signals obtained from the tape. Clearly, this delay period is unacceptable, since the scene itself may not be much longer than the delay period. Accordingly, there has been a real need for a video tape recording system in which synchronization is preserved between sequentially recorded scenes, without the penalty of a large delay time prior to the recording of each scene. The present invention fulfills this need.